Multiparametric Prostate MRI Accuracy of Prostate Imaging Reporting and Data System (v2.1) Scores 4 and 5: The Influence of Image Quality According to the Prostate Imaging Quality Score

Purpose: The accuracy of multiparametric magnetic resonance imaging (mpMRI) heavily relies on image quality, as evidenced by the evolution of the prostate imaging quality (PI-QUAL) scoring system for the evaluation of clinically significant prostate cancer (csPC). This study aims to evaluate the impact of PI-QUAL scores in detecting csPC within PI-RADS 4 and 5 lesions. Methods: We retrospectively selected from our database all mpMRI performed from January 2019 to March 2022. Inclusion criteria were as follows: (1) mpMRI acquired in our institution according to the technical requirements from the PI-RADS (v2.1) guidelines; (2) single lesion scored as PI-RADS (v2.1) 4 or 5; (3) MRI-TBx performed in our institution; (4) complete histology report; and (5) complete clinical record. Results: A total of 257 male patients, mean age 70.42 ± 7.6 years, with a single PI-RADS 4 or 5 lesion undergoing MRI-targeted biopsy, were retrospectively studied. Of these, 61.5% were PI-RADS 4, and 38.5% were PI-RADS 5, with 84% confirming neoplastic cells. In high-quality image lesions (PI-QUAL ≥ 4), all PI-RADS 5 lesions were accurately identified as positive at the final histological examination (100% of CDR). For PI-RADS 4 lesions, 37 (23%) were negative, resulting in a cancer detection rate of 77% (95% CI: 67.51–84.83). Conclusions: The accuracy of mpMRI, independently of the PI-RADS score, progressively decreased according to the decreasing PI-QUAL score. These findings emphasize the crucial role of the PI-QUAL scoring system in evaluating PI-RADS 4 and 5 lesions, influencing mpMRI accuracy.

Abstract: Purpose: The accuracy of multiparametric magnetic resonance imaging (mpMRI) heavily relies on image quality, as evidenced by the evolution of the prostate imaging quality (PI-QUAL) scoring system for the evaluation of clinically significant prostate cancer (csPC).This study aims to evaluate the impact of PI-QUAL scores in detecting csPC within PI-RADS 4 and 5 lesions.Methods: We retrospectively selected from our database all mpMRI performed from January 2019 to March 2022.Inclusion criteria were as follows: (1) mpMRI acquired in our institution according to the technical requirements from the PI-RADS (v2.1) guidelines; (2) single lesion scored as PI-RADS (v2.1) 4 or 5; (3) MRI-TBx performed in our institution; (4) complete histology report; and (5) complete clinical record.Results: A total of 257 male patients, mean age 70.42 ± 7.6 years, with a single PI-RADS 4 or 5 lesion undergoing MRI-targeted biopsy, were retrospectively studied.Of these, 61.5% were PI-RADS 4, and 38.5% were PI-RADS 5, with 84% confirming neoplastic cells.In high-quality image lesions (PI-QUAL ≥ 4), all PI-RADS 5 lesions were accurately identified as positive at the final histological examination (100% of CDR).For PI-RADS 4 lesions, 37 (23%) were negative, resulting in a cancer detection rate of 77% (95% CI: 67.51-84.83).Conclusions: The accuracy of mpMRI, independently of the PI-RADS score, progressively decreased according to the decreasing PI-QUAL score.These findings emphasize the crucial role of the PI-QUAL scoring system in evaluating PI-RADS 4 and 5 lesions, influencing mpMRI accuracy.Keywords: mpMRI; PI-RADS; PI-QUAL; prostate biopsy; prostate cancer

Purpose
Multiparametric magnetic resonance imaging (mpMRI) is a noninvasive exam widely recommended for the detection and stratification of clinically significant prostate cancer (csPCa) [1].
The MRI-targeted biopsy (MRI-TBx), meant as the fusion between mpMRI and transrectal ultrasound, has been demonstrated to significantly outperform systematic biopsy for the detection of prostate cancer (PCa) [2,3].
The standardization of the image acquisition technique and interpretation of mpRMI is codified by the Prostate Imaging Reporting and Data System (PI-RADS) [4].The latest PI-RADS 2.1 version has been demonstrated to outperform previous versions, reaching a sensitivity of 87% (95% CI 82-91%) and a specificity of 74% (95% CI 63-82%), with a progressive increase in the cancer detection rate (CDR) as the score increases from 1 to 5 (from 0.03 to 0.97) [5,6].However, there is increasing evidence that the performances of mpMRI is significantly influenced by image quality [7,8].For this reason, the prostate imaging quality (PI-QUAL) scoring system was developed based on both objective and subjective criteria, mainly influenced by the patient's characteristics [9].Since its introduction, the PI-QUAL scoring system has demonstrated good reproducibility and indicated that poor image quality is associated with a higher degree of uncertainty and lower accuracy [10][11][12].
Furthermore, a greater impact of the PI-QUAL scoring system on the classification of indeterminate lesions (PI-RADS 3) was recorded.It has been demonstrated that as the image quality increases, fewer lesions are classified as indeterminate and thus referred for biopsy [10,13].Moreover, considering the high negative predictive value of PI-RADS 1 and 2 (DFS 99.6% after 3 years and 94.1% after 6 years), independently of the image quality [14], there is still limited evidence on the impact of the PI-QUAL scoring system on the accuracy of PI-RADS 4 and 5.
The aim of the present study is to evaluate the impact of image quality, according to the PI-QUAL scoring system, on the ability to account for csPCa for PI-RADS 4 (csPCa likely to be present) and 5 (csPCa highly likely to be present), using the results of MRI-TBx as reference standard.

Materials and Methods
We retrospectively selected from our database all mpMRI performed from January 2019 to March 2022.Inclusion criteria were as follows: (1) mpMRI acquired in our institution according to the technical requirements from the PI-RADS (v2.1) guidelines; (2) single PI-RADS 4 or 5 lesion; (3) MRI-TBx performed in our institution; and (4) complete histology and clinical report.
All mpMRI were acquired on a 1.5 Tesla scanner (MAGNETOM ESSENZA, Siemens Healthcare, Erlangen, Germany) using a phased-array coil in a supine position (Table 1).All datasets were acquired according to the PI-RADS (v2.1) guidelines.
All patients received a fixed dose of contrast media (Gd-DOTA, DOTAREM ® 0.5 mmol/mL, Guerbet, Roissy CdG Cedex, France) using a fixed dose of 0.1 mmol/kg of body weight.
Reports were created by two expert radiologists at our institution according to the PI-RADS (v2.1) guidelines.Another two radiologists independently analyzed all datasets, evaluating the image quality according to the PI-QUAL score.
All prostate lesions scored as PI-RADS 4 or 5 underwent prostate biopsy.All biopsies were performed by an expert urologist using an MRI-TBx fusion device (Trinity ® ultrasound system, KOELIS, Meylan, France).
All patients received a fixed dose of contrast media (Gd-DOTA, DOTAREM ® 0.5 mmol/mL, Guerbet, Roissy CdG Cedex, France) using a fixed dose of 0.1 mmol/kg of body weight.
Reports were created by two expert radiologists at our institution according to the PI-RADS (v2.1) guidelines.Another two radiologists independently analyzed all datasets, evaluating the image quality according to the PI-QUAL score.
All prostate lesions scored as PI-RADS 4 or 5 underwent prostate biopsy.All biopsies were performed by an expert urologist using an MRI-TBx fusion device (Trinity ® ultrasound system, KOELIS, Meylan, France).
Before the procedure, mpMRIs were evaluated using software (ProMap Lite™ (Version 2024), KOELIS, Meylan, France) dedicated to 3D lesion semiautomatic segmentation on high-resolution T2-weighted images (Figure 1).Trans-perineal prostate biopsy was performed according to the European Association of Urology guidelines using a 16G needle and real-time synchronization of MR and US images.
An expert uropathologist reviewed all the specimens using the Gleason score (ISUP grade group classification system) [4].A Gleason score ≥ 6 was considered positive for PCa.
All continuous variables were expressed as mean ± standard deviation (SD) and categorical variables as counts and percentages.Trans-perineal prostate biopsy was performed according to the European Association of Urology guidelines using a 16G needle and real-time synchronization of MR and US images.
An expert uropathologist reviewed all the specimens using the Gleason score (ISUP grade group classification system) [4].A Gleason score ≥ 6 was considered positive for PCa.
All continuous variables were expressed as mean ± standard deviation (SD) and categorical variables as counts and percentages.
Differences between categorical variables, like PI-QUAL and PI-RADS categories, and the biopsy result (positive or negative) expressed as an absolute value or a percentage of CDR, were ruled out with a chi-square test.
The inter-reader agreement for PI-QUAL scoring was evaluated by means of weighted Cohen's kappa (κ) analysis.

Results
From a total of 786 mpMRI exams, all PI-RADS scores < 4 (374 patients) and multifocal prostate lesions (116 patients) were excluded.Among the 296 remaining patients, a total of 39 were excluded due to an absence of fusion biopsy (30), incomplete histology report (4), and incomplete clinical records (5).
Image quality was influenced by the presence of artifacts determined by the patients' characteristics.T2w images were all at least acceptable; for movement artifacts, radial k-space sampling was used or the sequence was repeated; for metal artifacts, the encoding phase direction was modified.DWI/ADC images were impaired in 78 patients (30.3% of the entire population).The cause of the impairment was determined by hip prosthesis (18; 23.1%), other metal devices (22; 28.2%), rectal air (23; 29.5%), and movement artifacts (15; 19.2%).DCE images were impaired in 95 patients (36.9% of the entire population).The cause of the impairment was determined by hip prostheses (18; 18.9%), other metal devices (28; 29.5%), rectal air (15; 15.8%), and movement artifacts (34; 35.8%).All PI-QUAL 2 (18) were determined by the presence of hip prostheses, which impaired the quality of both DWI and DCE.However, 25 patients with hip prostheses were enrolled in the study population, but 7 prostheses did not significantly impair the image quality due to the technical characteristics of the device.
When image quality was sufficient or below the minimum standard, a decrease in the CDR was observed (CDR 69.49%; 95% CI: 56.13-80.81),while the CDR for PI-RADS 4 and 5 was not significantly different (p-value: 0.06 and 0.205).

Discussion
The results confirmed the importance of mpMRI image quality for PI-RADS 4 and 5 lesions.According to the latest metanalysis, the CDR for PI-RADS 4 and 5 is 70% (95% CI: 61-79%) and 97% (95% CI: 92-99%), respectively, independently of image quality [6].Our results are in line with these outcomes since the overall CDR was 76.6% and 96% for PI-RADS 4 and 5, respectively.When CDR was stratified according to the PI-QUAL system, a heterogeneous scenario was observed.In PI-RADS 5 lesions, the CDR reached 100% when image quality was high (PI-QUAL ≥ 4), while it decreased to 92.3% for sufficient image quality (PI-QUAL 3) and 72.7% for image quality below the minimum standard (PI-QUAL ≤ 2).The same trend was observed for PI-RADS 4 lesions, where CDR reached 82.6% in high image quality, while it decreased to 64.3% for sufficient image quality and 42.8% for image quality below the minimum standard.That CDR reduces with the reduction of the PI-QUAL score was mainly due to the difficulty involved in contouring the prostate.These results are in line with the recently published data by Brembilla et al., confirming a decrease in the CDR from high image quality (PI-QUAL 4-5) to lower image quality (PI-QUAL 2-3) [13].
The results also confirmed the good reproducibility of the PI-QUAL scoring system.A good (k: 0.73) overall agreement was observed for all PI-QUAL categories, as well as for grouped categories (≥4, 3 and ≤2; k: 0.75, 0.72, and 0.78, respectively), in line with previous publications [11,15].
Furthermore, despite all exams being conducted in strict accordance with the PI-RADS 2.1 recommendations, the image quality was only sufficient or below the minimum standard in 15.9% and 7.1% of the exams, respectively.Thus, patient factors causing artifacts can impair image quality and the accuracy of mpMRI.
In fact, significant artifacts can lead to misreading potential target lesions.Poor image quality may not solely result from artifacts but could also stem from inherent MRI characteristics like magnet strength, hardware, and scanning sequences.Consequently, centers experiencing consistently low image quality may yield poorer results across various PIRADS categories, underscoring the importance of leveraging the PI-QUAL score to enhance image quality.
The first limitation of the study can be considered the use of a specialized radiologist in an academic environment since our results may not be reproducible when general radiologists are involved.Secondly, this was a retrospective study and may therefore have intrinsic limitations such as selection bias.

Table 3 .
Image quality and PI-QUAL score.

Table 4 .
PI-QUAL score distribution in positive (CDR) and negative (false positive) biopsies.